In recent years, attention has focused on a fuel cell that has a high energy conversion efficiency and does not generate a harmful material during a power generation reaction. As one example of such a fuel cell, a polymer electrolyte fuel cell operating at a low temperature of 100° C. or less is known.
The polymer electrolyte fuel cell has a fundamental structure in which a solid polymer membrane as an electrolyte membrane is disposed between an anode and a cathode. The polymer electrolyte fuel cell is a device where hydrogen is supplied to the anode, oxidant gas containing oxygen is supplied to the cathode, and power through the following electrochemical reaction is generated.Anode: H2→2H++2e−  (1)Cathode: ½O2+2H++2e−→H2O  (2)In the anode, the supplied hydrogen is decomposed into hydrogen ions and electrons as shown in formula (1). The hydrogen ions travel toward the cathode through the solid polymer electrolyte membrane, and the electrons travel to the anode through an external circuit. In the cathode, the oxygen contained in the oxidant gas supplied to the cathode reacts with the hydrogen ions and electrons that have traveled from the anode, thereby generating water as shown in formula (2). Thus, in the external circuit, the electrons travel from the anode to the cathode, and hence power can be taken out.
Particularly, the polymer electrolyte fuel cell has a lower operating temperature and a higher output density than those of other types of fuel cells. Recently, especially, the polymer electrolyte fuel cell has been expected to be applied to a power source of a mobile device and a power source of an on-vehicle device. As such a polymer electrolyte fuel cell, Patent Literature 1 discloses a fuel cell stack formed by stacking planar-array fuel cell layers each of which includes a plurality of membrane electrode assemblies arranged in a planar shape.